The present invention relates to a polymeric blend having improved properties and particularly suited for the use in the preparation of films. More particularly the present invention relates to such a polymeric blend having improved melt strength and particularly adapted to the preparation of blown films which may subsequently be laminated to metal substrates.
In U.S. Pat. No. 4,626,157 there are disclosed metal containers especially aerosol dispensing containers containing top can end members and valve cup members formed from a metal sheet material comprising a thin polymeric layer overlaid on the metallic substrate. Particularly suitable polymeric materials include polyesters and polypropylene (col. 4, lines 30-32). In U.S. Pat. No. 4,423,823 a similar metal can is disclosed wherein at least one component thereof is comprised of a metal sheet containing a laminate of polypropylene which is cast thereon.
In U.S. Pat. No. 4,034,132 a carboxyl modified polypropylene resin is proposed for adhering to enamel coated metal substrates.
In U.S. Pat. No. 4,686,152 a metal packaging foil comprising an iron foil and a polymeric resin coating is disclosed. Suitable polymeric resins including polypropylene, polyethylene, polybutene-1, a propylene/ethylene copolymer, etc. are disclosed at columns 11 and 12.
In U.S. Pat. No. 4,734,303 a laminate comprising an iron or steel foil having a plastic film layer adhered thereto with an adhesive force of at least 600 grams/15 millimeters of width is disclosed. The list of suitable films are those previously disclosed in 4,636,152 and are adhered by the use of an adhesive resin including isocyanate type and epoxy type adhesives (col. 10, lines 30-34).
In U.S. Pat. No. 4,361,020 a metal substrate having a plastic film adhered thereto is employed to prepare cold formed objects. Suitable plastics include oriented or nonoriented polyethylene terephthalate, polyimide resins, polypropylene, polycarbonate, and blends.
For the teachings contained therein the foregoing United States patents are incorporated in their entirety by reference thereto.
Highly desirable resin films comprising polypropylene or modified polypropylene are employed in the foregoing laminated structures due to the inherent chemical resistance of such resins. Disadvantageously however, presently available polypropylene and modified polypropylene resins are not well suited for the preparation of films, particularly by the use of the blown film technique. The alternative of employing casting technology to prepare such films does not readily permit the use of randomizing procedures to prepare a film of uniform gauge that is free of defects. Consequently, laminates prepared utilizing cast films of polypropylene may possess undesirable variations of thickness or other defects which may render such laminates unsuited for the intended use. In the formation of sealed metal containers as disclosed in certain of the foregoing prior art references, it is highly desirable to provide a film of uniform dimension such as may be prepared by the blown film technique.
The blown film technique involves use of air to expand a molten bubble of polymer. The technique is well known in the art and taught in U.S. Pat. Nos. 3,650,649, 3,801,429 and 3,354,506, the teachings of which are incorporated herein by reference thereto. Polypropylene resins have also been found to be particularly difficult to adhere to various metallic substrates particularly by the use of thermoplastic adhesive resins. Various commercial embodiments of the foregoing laminates and structures comprising such laminates have utilized solvent born adhesives such as lacquers to laminate the cast polypropylene film to the metallic substrate. The use of such solvent-based adhesives involves unnecessary complexity in the preparation of laminates and is undesirable from the standpoint of environmental degradation due to solvent emissions.
It would be desirable if there were provided an improved polypropylene containing resin for use in the preparation of laminated structures
Furthermore it would be desirable if there were provided such a resin having improved melt strength thereby allowing its use in the preparation of blown films therefrom without the loss of solvent resistance and other resin properties normally attributable to polypropylene resins.
It would additionally be desirable if there were provided a polypropylene containing resin having improved compatibility with thermoplastic adhesive resins for use in the preparation of laminated structures comprising a layer of such polypropylene containing resin and a layer of thermoplastic adhesive resin.
Finally it would be desirable if there were provided an improved metallic laminate containing a metallic substrate having laminated thereto an improved polypropylene based resin which could be readily formed into components for containers.